Carbaryl

63-25-2

Hazard Summary-Created in April 1992; Revised in January 2000

Carbaryl is an insecticide used on a variety of crops. Acute (short-term)
and chronic (long-term) occupational exposure of humans to carbaryl has
been observed to cause cholinesterase inhibition, and reduced levels of
this enzyme in the blood cause neurological effects. These effects
appear to be reversible upon discontinuation of exposure. Headaches,
memory loss, muscle weakness and cramps, and anorexia are caused by prolonged
low-level exposure to carbaryl resulting from cholinesterase inhibition.
EPA has classified carbaryl as a Group D, not classifiable as to human
carcinogenicity.

Acute carbaryl exposure in humans may also cause eye and skin irritation.
(1)

Tests involving acute exposure of rats, mice, rabbits, and guinea
pigs have demonstrated carbaryl to have moderate
to high acute toxicity from ingestion
and moderate acute toxicity from dermal
exposure. (5)

Chronic Effects (Noncancer):

Chronic exposure to carbaryl results in cholinesterase inhibition,
which is reversible upon discontinuation of exposure. Headaches,
memory loss, muscle weakness and cramps, and anorexia are caused by
prolonged low-level exposure of humans to carbaryl resulting from cholinesterase
inhibition. (4)

Kidney and liver effects have been observed in rats chronically exposed
to carbaryl by ingestion. (2,6)

EPA has not established a Reference Concentration (RfC)
for carbaryl. (6)

The Reference Dose (RfD)
for carbaryl is 0.1 milligrams per kilogram body weight per day (mg/kg/d)
based on kidney and liver toxicity in rats. The RfD
is an estimate (with uncertainty spanning perhaps an order of magnitude)
of a daily oral exposure to the human population (including sensitive
subgroups) that is likely to be without appreciable risk of deleterious
noncancer effects during a lifetime. It is not a direct estimator
of risk but rather a reference point to gauge the potential effects.
At exposures increasingly greater than the RfD,
the potential for adverse health effects increases. Lifetime exposure
above the RfD does not imply
that an adverse health effect would necessarily occur. (6)

EPA has medium confidence in the RfD
based on: high confidence in the critical study because it was well
designed and clearly reported with unequivocal effects levels established;
and medium confidence in the database because it is moderately supportive
of the nature of the critical effect. (6)

Reproductive/Developmental Effects:

No information is available on the reproductive or developmental
effects of carbaryl in humans.

Two studies produced teratogenic effects in dogs fed carbaryl, but
dogs were judged inappropriate for human health risk assessment because
of differences in metabolism. Other studies demonstrating teratogenic
effects also caused maternal toxicity. (2,6)

Reduced fertility and litter size and increased mortality in offspring
have been observed in rats exposed to carbaryl in their diet over three
generations. (2)

Cancer Risk:

No information is available on the carcinogenic effects of carbaryl
in humans.

No significant increase in tumor incidence was found among exposed
animals in several studies. (4)

Health Data from Inhalation Exposure

ACGIH TLV--American Conference of Governmental and Industrial
Hygienists' threshold limit value expressed as a time-weighted average;
the concentration of a substance to which most workers can be exposed
without adverse effects. NIOSH IDLH--National Institute of Occupational Safety and Health's
immediately dangerous to life or health concentration; NIOSH recommended
exposure limit to ensure that a worker can escape from an exposure condition
that is likely to cause death or immediate or delayed permanent adverse
health effects or prevent escape from the environment. NIOSH REL--National Institute of Occupational Safety and Health's
recommended exposure limit; NIOSH-recommended exposure limit for an 8-
or 10-h time-weighted-average exposure and/or ceiling. OSHA PEL--Occupational Safety and Health Administration's permissible
exposure limit expressed as a time-weighted average; the concentration
of a substance to which most workers can be exposed without adverse effect
averaged over a normal 8-h workday or a 40-h workweek.

The health and regulatory values cited in this factsheet were obtained
in December 1999.aHealth numbers are toxicological numbers
from animal testing or risk assessment values developed by EPA. bRegulatory numbers are values that have been
incorporated in Government regulations, while advisory numbers are nonregulatory
values provided by the Government or other groups as advice. OSHA
numbers are regulatory, whereas NIOSH and ACGIH numbers are advisory.

International Agency for Research on Cancer (IARC).
IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals
to Man: Some Carbamates, Thiocarbamates and Carbazides. Volume 12.
World Health Organization, Lyon. 1976.

National Institute for Occupational Safety and
Health (NIOSH). Pocket
Guide to Chemical Hazards. U.S. Department of Health and Human
Services, Public Health Service, Centers for Disease Control and Prevention.
Cincinnati, OH. 1997.